In the wheel hubs of the aforesaid type, the mentioned frontal toothing has the purpose of coupling head-to-head the inner ring of the wheel hub and a corresponding frontal toothing of an outer ring of a constant velocity joint, to ensure the torque transmission from the constant velocity joint to the inner ring of the wheel hub, which carries a wheel of the vehicle by means of a flanged end thereof. A coupling of this type is described in U.S. Pat. No. 4,893,960, which also teaches how to make the frontal toothing on the inner ring of the wheel hub. In particular, the frontal toothing is obtained using the so-called “orbital forming” method simultaneously with the forming of the upset collar by means of a tool including a truncated-cone-shaped element which upsets the collar and a frontally toothed tubular element, axially slidingly mounted on the truncated-cone-shaped element, which impresses the toothing onto the collar still during the step of deforming. A radially outer element of the toothed tubular element, which may either belong to the same tool or be a second separate tool, controls the radially outward deformation of the collar.
Although a forming method like that described in U.S. Pat. No. 4,893,960 is satisfactory, it requires the use of a relatively complex tool and especially does not provide toothings with features of absolute tooth profile constancy, which feature is absolutely necessary nowadays in view of the ever increasing transmitted torques.
It is thus the object of the present invention to provide a method of forming a frontal toothing on an inner ring of a wheel hub by means of plastic deformation, which is an alternative to the methods of the prior art, and in particular is capable of ensuring a higher dimensional accuracy of the teeth and maintaining a high dimensional and geometrical constancy in the profile of the teeth themselves.